<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xmlns:dubbo="http://dubbo.apache.org/schema/dubbo"
       xmlns="http://www.springframework.org/schema/beans" xmlns:context="http://www.springframework.org/schema/context"
       xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd
       http://dubbo.apache.org/schema/dubbo http://dubbo.apache.org/schema/dubbo/dubbo.xsd http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context.xsd">
    <context:property-placeholder/>
    <dubbo:application name="serialization-java-consumer">
        <dubbo:parameter key="qos.enable" value="true" />
        <dubbo:parameter key="qos.accept.foreign.ip" value="false" />
        <dubbo:parameter key="qos.port" value="33333" />
    </dubbo:application>
    <dubbo:registry address="zookeeper://${zookeeper.address:127.0.0.1}:2181"/>
    <dubbo:reference id="demoService" check="true" interface="org.apache.dubbo.samples.serialization.api.DemoService"/>
</beans>

public class DubboConsumer {
    public static void main(String[] args) {
        ClassPathXmlApplicationContext context = new ClassPathXmlApplicationContext("spring/dubbo-demo-consumer.xml");
        context.start();
        DemoService demoService = context.getBean("demoService", DemoService.class);
        String hello = demoService.sayHello("world");
        System.out.println(hello);
    }
}

    @Override
    public Object getObject() {
        return get();
    }

    public synchronized T get() {
        if (destroyed) {
            throw new IllegalStateException("The invoker of ReferenceConfig(" + url + ") has already destroyed!");
        }
        // 代理引用如果是空的，調(diào)用init
        if (ref == null) {
            init();
        }
        return ref;
    }
    public synchronized void init() {
        if (initialized) {
            return;
        }
        if (bootstrap == null) {
            bootstrap = DubboBootstrap.getInstance();
            bootstrap.init();
        }
        // 1. 檢查配置ConsumerConfig，有的話檢查配置，沒(méi)有就新建一個(gè)ConsumerConfig
        // 2. 反射創(chuàng)建調(diào)用的API
        // 3. 初始化ServiceMetadata
        // 4. 注冊(cè)Consumer
        // 5. 檢查ReferenceConfig，RegistryConfig，ConsumerConfig
        checkAndUpdateSubConfigs();
        checkStubAndLocal(interfaceClass);
        // 檢查引用的接口是否mock
        ConfigValidationUtils.checkMock(interfaceClass, this);
        // consumer的信息
        Map<String, String> map = new HashMap<String, String>();
        map.put(SIDE_KEY, CONSUMER_SIDE);
        // 添加運(yùn)行時(shí)參數(shù)到map，包括：dubbo，release，timestamp，pid
        ReferenceConfigBase.appendRuntimeParameters(map);
        // 是不是泛化，不是的話進(jìn)入條件
        if (!ProtocolUtils.isGeneric(generic)) {
            String revision = Version.getVersion(interfaceClass, version);
            if (revision != null && revision.length() > 0) {
                map.put(REVISION_KEY, revision);
            }
            // 獲取方法，生成包裝類，使用javassist，將生成的類放到WRAPPER_MAP中，key是org.apache.dubbo.samples.serialization.api.DemoService類對(duì)象，value是包裝類的實(shí)例
            String[] methods = Wrapper.getWrapper(interfaceClass).getMethodNames();
            if (methods.length == 0) {
                logger.warn("No method found in service interface " + interfaceClass.getName());
                map.put(METHODS_KEY, ANY_VALUE);
            } else {
                // method放到map，這里method是sayHello
                map.put(METHODS_KEY, StringUtils.join(new HashSet<String>(Arrays.asList(methods)), COMMA_SEPARATOR));
            }
        }
        // interface org.apache.dubbo.samples.serialization.api.DemoService
        map.put(INTERFACE_KEY, interfaceName);
        // 追加其他參數(shù)到map中
        AbstractConfig.appendParameters(map, getMetrics());
        AbstractConfig.appendParameters(map, getApplication());
        AbstractConfig.appendParameters(map, getModule());
        // remove 'default.' prefix for configs from ConsumerConfig
        // appendParameters(map, consumer, Constants.DEFAULT_KEY);
        AbstractConfig.appendParameters(map, consumer);
        AbstractConfig.appendParameters(map, this);
        MetadataReportConfig metadataReportConfig = getMetadataReportConfig();
        if (metadataReportConfig != null && metadataReportConfig.isValid()) {
            map.putIfAbsent(METADATA_KEY, REMOTE_METADATA_STORAGE_TYPE);
        }
        Map<String, AsyncMethodInfo> attributes = null;
        if (CollectionUtils.isNotEmpty(getMethods())) {
            attributes = new HashMap<>();
            for (MethodConfig methodConfig : getMethods()) {
                AbstractConfig.appendParameters(map, methodConfig, methodConfig.getName());
                String retryKey = methodConfig.getName() + ".retry";
                if (map.containsKey(retryKey)) {
                    String retryValue = map.remove(retryKey);
                    if ("false".equals(retryValue)) {
                        map.put(methodConfig.getName() + ".retries", "0");
                    }
                }
                AsyncMethodInfo asyncMethodInfo = AbstractConfig.convertMethodConfig2AsyncInfo(methodConfig);
                if (asyncMethodInfo != null) {
//                    consumerModel.getMethodModel(methodConfig.getName()).addAttribute(ASYNC_KEY, asyncMethodInfo);
                    attributes.put(methodConfig.getName(), asyncMethodInfo);
                }
            }
        }
        String hostToRegistry = ConfigUtils.getSystemProperty(DUBBO_IP_TO_REGISTRY);
        if (StringUtils.isEmpty(hostToRegistry)) {
            hostToRegistry = NetUtils.getLocalHost();
        } else if (isInvalidLocalHost(hostToRegistry)) {
            throw new IllegalArgumentException("Specified invalid registry ip from property:" + DUBBO_IP_TO_REGISTRY + ", value:" + hostToRegistry);
        }
        map.put(REGISTER_IP_KEY, hostToRegistry);
        // 所有數(shù)據(jù)在存到serviceMetadata的attachments中
        serviceMetadata.getAttachments().putAll(map);
        // 創(chuàng)建Service代理
        ref = createProxy(map);
        // 設(shè)置ServiceMetadata的Service代理引用
        serviceMetadata.setTarget(ref);
        serviceMetadata.addAttribute(PROXY_CLASS_REF, ref);
        ConsumerModel consumerModel = repository.lookupReferredService(serviceMetadata.getServiceKey());
        consumerModel.setProxyObject(ref);
        consumerModel.init(attributes);
        // 標(biāo)記初始化完畢
        initialized = true;
        // dispatch a ReferenceConfigInitializedEvent since 2.7.4
        dispatch(new ReferenceConfigInitializedEvent(this, invoker));
    }

    @SuppressWarnings({"unchecked", "rawtypes", "deprecation"})
    private T createProxy(Map<String, String> map) {
        // 是否是InJvm，協(xié)議是InJvm
        if (shouldJvmRefer(map)) {
            URL url = new URL(LOCAL_PROTOCOL, LOCALHOST_VALUE, 0, interfaceClass.getName()).addParameters(map);
            invoker = REF_PROTOCOL.refer(interfaceClass, url);
            if (logger.isInfoEnabled()) {
                logger.info("Using injvm service " + interfaceClass.getName());
            }
        } else {
            urls.clear();
            if (url != null && url.length() > 0) { // user specified URL, could be peer-to-peer address, or register center's address.
                String[] us = SEMICOLON_SPLIT_PATTERN.split(url);
                if (us != null && us.length > 0) {
                    for (String u : us) {
                        URL url = URL.valueOf(u);
                        if (StringUtils.isEmpty(url.getPath())) {
                            url = url.setPath(interfaceName);
                        }
                        if (UrlUtils.isRegistry(url)) {
                            urls.add(url.addParameterAndEncoded(REFER_KEY, StringUtils.toQueryString(map)));
                        } else {
                            urls.add(ClusterUtils.mergeUrl(url, map));
                        }
                    }
                }
            } else { // assemble URL from register center's configuration
                // 如果protocols不是injvm檢查注冊(cè)中心
                if (!LOCAL_PROTOCOL.equalsIgnoreCase(getProtocol())) {
                    checkRegistry();
                    // url列表，將zookeeper://改成registry://
                    List<URL> us = ConfigValidationUtils.loadRegistries(this, false);
                    if (CollectionUtils.isNotEmpty(us)) {
                        for (URL u : us) {
                            // 監(jiān)控URL
                            URL monitorUrl = ConfigValidationUtils.loadMonitor(this, u);
                            // 如果有監(jiān)控配置放到map中
                            if (monitorUrl != null) {
                                map.put(MONITOR_KEY, URL.encode(monitorUrl.toFullString()));
                            }
                            // 根據(jù)map中的信息生成url，這里生成的結(jié)果是
                            /*
                            registry://127.0.0.1:2181/org.apache.dubbo.registry.RegistryService?application=serialization-java-consumer&dubbo=2.0.2&pid=66793&qos.accept.foreign.ip=false&qos.enable=true&qos.port=33333&refer=application%3Dserialization-java-consumer%26check%3Dtrue%26dubbo%3D2.0.2%26init%3Dfalse%26interface%3Dorg.apache.dubbo.samples.serialization.api.DemoService%26methods%3DsayHello%26pid%3D66793%26qos.accept.foreign.ip%3Dfalse%26qos.enable%3Dtrue%26qos.port%3D33333%26register.ip%3D192.168.58.45%26release%3D2.7.7%26side%3Dconsumer%26sticky%3Dfalse%26timestamp%3D1636532992568&registry=zookeeper&release=2.7.7&timestamp=1636533091883
                            */
                            urls.add(u.addParameterAndEncoded(REFER_KEY, StringUtils.toQueryString(map)));
                        }
                    }
                    if (urls.isEmpty()) {
                        throw new IllegalStateException("No such any registry to reference " + interfaceName + " on the consumer " + NetUtils.getLocalHost() + " use dubbo version " + Version.getVersion() + ", please config <dubbo:registry address=\"...\" /> to your spring config.");
                    }
                }
            }
            // 如果引用的URL就1個(gè)直接通過(guò)refer引用服務(wù)，這里和export相似，通過(guò)調(diào)用鏈實(shí)現(xiàn)的
            // - ProtocolListenerWrapper
            // - - ProtocolFilterWrapper
            // - - - RegistryProtocol
            if (urls.size() == 1) {
                // 通過(guò)RegistryProtocol#refer引用服務(wù)
                invoker = REF_PROTOCOL.refer(interfaceClass, urls.get(0));
            } else {
                // 如果是引用的服務(wù)多個(gè)，循環(huán)處理
                List<Invoker<?>> invokers = new ArrayList<Invoker<?>>();
                URL registryURL = null;
                for (URL url : urls) {
                    invokers.add(REF_PROTOCOL.refer(interfaceClass, url));
                    if (UrlUtils.isRegistry(url)) {
                        registryURL = url; // use last registry url
                    }
                }
                if (registryURL != null) { // registry url is available
                    // for multi-subscription scenario, use 'zone-aware' policy by default
                    // 集群處理
                    URL u = registryURL.addParameterIfAbsent(CLUSTER_KEY, ZoneAwareCluster.NAME);
                    // The invoker wrap relation would be like: ZoneAwareClusterInvoker(StaticDirectory) -> FailoverClusterInvoker(RegistryDirectory, routing happens here) -> Invoker
                    // 加入到集群中，這里包含集中集群處理模式，分別是：
                    invoker = CLUSTER.join(new StaticDirectory(u, invokers));
                } else { // not a registry url, must be direct invoke.
                    invoker = CLUSTER.join(new StaticDirectory(invokers));
                }
            }
        }
        // invoer不可用處理
        if (shouldCheck() && !invoker.isAvailable()) {
            invoker.destroy();
            throw new IllegalStateException("Failed to check the status of the service "
                    + interfaceName
                    + ". No provider available for the service "
                    + (group == null ? "" : group + "/")
                    + interfaceName +
                    (version == null ? "" : ":" + version)
                    + " from the url "
                    + invoker.getUrl()
                    + " to the consumer "
                    + NetUtils.getLocalHost() + " use dubbo version " + Version.getVersion());
        }
        if (logger.isInfoEnabled()) {
            logger.info("Refer dubbo service " + interfaceClass.getName() + " from url " + invoker.getUrl());
        }
        /**
         * @since 2.7.0
         * ServiceData存儲(chǔ)，SPI機(jī)制，支持內(nèi)存和遠(yuǎn)程兩種方式
         */
        String metadata = map.get(METADATA_KEY);
        WritableMetadataService metadataService = WritableMetadataService.getExtension(metadata == null ? DEFAULT_METADATA_STORAGE_TYPE : metadata);
        if (metadataService != null) {
            URL consumerURL = new URL(CONSUMER_PROTOCOL, map.remove(REGISTER_IP_KEY), 0, map.get(INTERFACE_KEY), map);
            metadataService.publishServiceDefinition(consumerURL);
        }
        // create service proxy
        return (T) PROXY_FACTORY.getProxy(invoker, ProtocolUtils.isGeneric(generic));
    }

    @Override
    @SuppressWarnings("unchecked")
    public <T> Invoker<T> refer(Class<T> type, URL url) throws RpcException {
        // 注冊(cè)中心url 將 registry:// 轉(zhuǎn)成 zookeeper://
        url = getRegistryUrl(url);
        // 獲取注冊(cè)中心
        Registry registry = registryFactory.getRegistry(url);
        if (RegistryService.class.equals(type)) {
            return proxyFactory.getInvoker((T) registry, type, url);
        }
        // 從url中解析出引用服務(wù)信息
        Map<String, String> qs = StringUtils.parseQueryString(url.getParameterAndDecoded(REFER_KEY));
        // 獲取分組
        String group = qs.get(GROUP_KEY);
        // 如果設(shè)置分組了，那么使用MergeableCluster策略
        if (group != null && group.length() > 0) {
            if ((COMMA_SPLIT_PATTERN.split(group)).length > 1 || "*".equals(group)) {
                return doRefer(getMergeableCluster(), registry, type, url);
            }
        }
        return doRefer(cluster, registry, type, url);
    }

    private <T> Invoker<T> doRefer(Cluster cluster, Registry registry, Class<T> type, URL url) {
        // 獲取集群目錄Directory，代表Invoker的集合
        RegistryDirectory<T> directory = new RegistryDirectory<T>(type, url);
        directory.setRegistry(registry);
        directory.setProtocol(protocol);
        // all attributes of REFER_KEY
        Map<String, String> parameters = new HashMap<String, String>(directory.getConsumerUrl().getParameters());
        URL subscribeUrl = new URL(CONSUMER_PROTOCOL, parameters.remove(REGISTER_IP_KEY), 0, type.getName(), parameters);
        if (directory.isShouldRegister()) {
            directory.setRegisteredConsumerUrl(subscribeUrl);
            // 注冊(cè)消費(fèi)者url
            registry.register(directory.getRegisteredConsumerUrl());
        }
        directory.buildRouterChain(subscribeUrl);
        // 向ZK發(fā)起訂閱服務(wù)，并設(shè)置監(jiān)聽，這里比較復(fù)雜，最終會(huì)在ZookeeperRegistry#doSubscribe做服務(wù)訂閱
        directory.subscribe(toSubscribeUrl(subscribeUrl));
        // 加入集群
        Invoker<T> invoker = cluster.join(directory);
        List<RegistryProtocolListener> listeners = findRegistryProtocolListeners(url);
        if (CollectionUtils.isEmpty(listeners)) {
            return invoker;
        }
        RegistryInvokerWrapper<T> registryInvokerWrapper = new RegistryInvokerWrapper<>(directory, cluster, invoker, subscribeUrl);
        for (RegistryProtocolListener listener : listeners) {
            listener.onRefer(this, registryInvokerWrapper);
        }
        return registryInvokerWrapper;
    }

    @Override
    public void doSubscribe(final URL url, final NotifyListener listener) {
        try {
            if (ANY_VALUE.equals(url.getServiceInterface())) {
                String root = toRootPath();
                // 初始化監(jiān)聽
                ConcurrentMap<NotifyListener, ChildListener> listeners = zkListeners.computeIfAbsent(url, k -> new ConcurrentHashMap<>());
                ChildListener zkListener = listeners.computeIfAbsent(listener, k -> (parentPath, currentChilds) -> {
                    for (String child : currentChilds) {
                        child = URL.decode(child);
                        if (!anyServices.contains(child)) {
                            anyServices.add(child);
                            subscribe(url.setPath(child).addParameters(INTERFACE_KEY, child,
                                    Constants.CHECK_KEY, String.valueOf(false)), k);
                        }
                    }
                });
                // 創(chuàng)建zk節(jié)點(diǎn)
                zkClient.create(root, false);
                List<String> services = zkClient.addChildListener(root, zkListener);
                if (CollectionUtils.isNotEmpty(services)) {
                    for (String service : services) {
                        service = URL.decode(service);
                        anyServices.add(service);
                        subscribe(url.setPath(service).addParameters(INTERFACE_KEY, service,
                                Constants.CHECK_KEY, String.valueOf(false)), listener);
                    }
                }
            } else {
                List<URL> urls = new ArrayList<>();
                for (String path : toCategoriesPath(url)) {
                    ConcurrentMap<NotifyListener, ChildListener> listeners = zkListeners.computeIfAbsent(url, k -> new ConcurrentHashMap<>());
                    ChildListener zkListener = listeners.computeIfAbsent(listener, k -> (parentPath, currentChilds) -> ZookeeperRegistry.this.notify(url, k, toUrlsWithEmpty(url, parentPath, currentChilds)));
                    zkClient.create(path, false);
                    List<String> children = zkClient.addChildListener(path, zkListener);
                    if (children != null) {
                        urls.addAll(toUrlsWithEmpty(url, path, children));
                    }
                }
                // 
                notify(url, listener, urls);
            }
        } catch (Throwable e) {
            throw new RpcException("Failed to subscribe " + url + " to zookeeper " + getUrl() + ", cause: " + e.getMessage(), e);
        }
    }

    @Override
    public <T> Invoker<T> protocolBindingRefer(Class<T> serviceType, URL url) throws RpcException {
        optimizeSerialization(url);
        // 創(chuàng)建RPC Invoker，通過(guò)getClients(url)創(chuàng)建網(wǎng)絡(luò)客戶端
        DubboInvoker<T> invoker = new DubboInvoker<T>(serviceType, url, getClients(url), invokers);
        // 將invoker添加到invokers中
        invokers.add(invoker);
        return invoker;
    }
    // 創(chuàng)建客戶端數(shù)組
    private ExchangeClient[] getClients(URL url) {
        // whether to share connection
        // 是否共享鏈接
        boolean useShareConnect = false;
        int connections = url.getParameter(CONNECTIONS_KEY, 0);
        List<ReferenceCountExchangeClient> shareClients = null;
        // if not configured, connection is shared, otherwise, one connection for one service
        if (connections == 0) {
            useShareConnect = true;
            /*
             * The xml configuration should have a higher priority than properties.
             * xml配置優(yōu)先級(jí)高于properties配置
             */
            String shareConnectionsStr = url.getParameter(SHARE_CONNECTIONS_KEY, (String) null);
            connections = Integer.parseInt(StringUtils.isBlank(shareConnectionsStr) ? ConfigUtils.getProperty(SHARE_CONNECTIONS_KEY,
                    DEFAULT_SHARE_CONNECTIONS) : shareConnectionsStr);
            // 共享鏈接客戶端
            shareClients = getSharedClient(url, connections);
        }
        // 創(chuàng)建ExchangeClient
        ExchangeClient[] clients = new ExchangeClient[connections];
        for (int i = 0; i < clients.length; i++) {
            if (useShareConnect) {
                // 從共享客戶端獲取
                clients[i] = shareClients.get(i);
            } else {
                // 初始化客戶端
                clients[i] = initClient(url);
            }
        }
        return clients;
    }
    // 初始化客戶端
    private ExchangeClient initClient(URL url) {
        // client type setting.
        String str = url.getParameter(CLIENT_KEY, url.getParameter(SERVER_KEY, DEFAULT_REMOTING_CLIENT));
        url = url.addParameter(CODEC_KEY, DubboCodec.NAME);
        // enable heartbeat by default
        url = url.addParameterIfAbsent(HEARTBEAT_KEY, String.valueOf(DEFAULT_HEARTBEAT));
        // BIO is not allowed since it has severe performance issue.
        if (str != null && str.length() > 0 && !ExtensionLoader.getExtensionLoader(Transporter.class).hasExtension(str)) {
            throw new RpcException("Unsupported client type: " + str + "," +
                    " supported client type is " + StringUtils.join(ExtensionLoader.getExtensionLoader(Transporter.class).getSupportedExtensions(), " "));
        }
        ExchangeClient client;
        try {
            // connection should be lazy
            if (url.getParameter(LAZY_CONNECT_KEY, false)) {
                // 延遲加載客戶端
                client = new LazyConnectExchangeClient(url, requestHandler);
            } else {
                // 通過(guò)NettyTransporter connect創(chuàng)建客戶端 與provider建立連接
                client = Exchangers.connect(url, requestHandler);
            }
        } catch (RemotingException e) {
            throw new RpcException("Fail to create remoting client for service(" + url + "): " + e.getMessage(), e);
        }
        return client;
    }